OBJECTIVE — To compare total retinal blood flow in diabetic patients with no or mild nonproliferative diabetic retinopathy and healthy control subjects and to investigate in patients whether there is a difference between retinal blood flow before morning insulin and under normoglycemic conditions using a glucose clamp. RESEARCH DESIGN AND METHODS — Twenty patients with type 1 diabetes with no or mild diabetic retinopathy were included in this open parallel-group study, and 20 healthy ageand sex-matched subjects were included as control subjects. Retinal blood flow was assessed by combining velocity measurements using laser Doppler velocimetry and diameter measurements using a commercially available dynamic vessel analyzer. Measurements were performed before and during a euglycemic clamp. RESULTS — Total retinal blood flow was higher in diabetic patients (53 � 16 �l/min) than in healthy subjects (43 � 16 �l/min; P � 0.034 between groups). When plasma glucose in diabetic patients was reduced from 9.3 � 1.7 to 5.3 � 0.5 mmol/l (P � 0.001) retinal blood flow decreased to 49 � 15 �l/min (P � 0.0003 vs. baseline). Total retinal blood flow during the glucose clamp was not significantly different from blood flow in normal control subjects (P
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